This invention relates generally to package wrapping machines and, more particularly, to an improved film cutter for severing sheets of soft stretch film from a continuous source of such film for use in a package wrapping machine.
A popular design of wrapping machine provides for wrapping packages, particularly articles supported on trays, by elevating the packages into stretched film sheets. The film sheets are severed from a continuous source of film by means of a pivotally mounted, cam actuated knife blade. The knife blade includes an upwardly extending serrated cutting edge which is reciprocated through film drawn from the film source. A bracket mounted above the drawn film defines a channel into which the knife blade is inserted to sever a film sheet from the continuous source of film. Such a wrapping machine is fully described in U.S. Pat. No. 4,510,731, and entitled "Film Wrapping Machine Including Film Length Selection," which is assigned to the same assignee as the present application and is incorporated herein by reference.
Film used by the wrapping machine is very soft and stretchy to permit proper wrapping of a package by the machine. Unfortunately, the soft, stretchy characteristics of the film necessary for a good wrap tend to make cutting or severing a film sheet from the continuous source difficult. The serrated cutting edge of the knife blade defines sharp cutting points which initially pierce the film and thereby facilitate cutting or tearing of the film along the length of the cutting blade.
While the prior art film cutter has performed well with films commonly used by the machine, such as films made of polyvinyl chloride, some cutting problems have occurred. Since better and less expensive films are always in demand to improve the art of package wrapping, new films which are more durable and even stretchier have been introduced by film manufacturers. The new films may be produced using different film making techniques or may be made from different materials, such as polyethylene. In any event, such new films tend to be harder to sever and increase the cutting problems encountered when using the prior art film cutter.
Various clamping arrangements can be envisioned by those skilled in the art to ensure that a film sheet is severed from the continuous source of film. However, such clamping arrangements tend to be mechanically complicated, expensive and can produce frictional problems in the operation of the film cutter leading to wear or damage of the driving mechanism for the cutter.
It is thus apparent that the need exists for an improved film cutter to be used on package wrapping machines wherein soft stretch film is drawn from a continuous source and severed into sheets to be wrapped about packages by the wrapping machine. To be effective, the improved film cutter must be reliable, inexpensive and, preferably, be easily incorporated into existing wrapping machines to permit the use of a larger variety of films by the machines.